What is this dial plug thing?

It's plumbed up to the fuel pressure reg iirc, I don't believe that's I dial

Copied from an evo forum
Without looking it up in the manual I don't know what pressure the fuel pressureregulator on an Evo maintains. So, lets say, for the sake of this discussion, it maintains 40 psi. Now this is 40 psi above whatever the manifold pressure is. So if manifold pressure is 10 psi vacuum then fuel pressure is actually 30 psi.

What the solenoid does is vent the fuel pressure regulator to atmosphere and the regulator now does not see manifold pressure. So, with the 10 psi manifold vacuum you still get 40 psi from the fuel pressure regulator. The solenoid is triggered during hot start and is intended to clear out fuel vapor that may have accumulated in the line.
 
Its just a cap, for an open port in the fuel pressure solenoid from memory
 
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